In the datasource definition there is a column Value_tx , value_nr, value_dt (text,number,date).
can you put in here the field containing the value it should use in the format <panel name="">.<field_name> or even a static value. I tried that but I could not get a an expected result.

There is a Default Value section in the Datasource edit dialog, under the Bind Variables tab, are you mentioning this section? Or the problem is related with your datasource definition query? Can you provide an example?

You can only use static values as default value_tx, value_nr and value_dt values of the bind variables. If you cannot get the exptected result, can provide an example datasource definition query and the static value of the bind variable?